NVME - reference manual online

NVM Express core driver.

Chapter

March 18, 2014

NVME(4) BSD Kernel Interfaces Manual NVME(4)NAME
nvme — NVM Express core driver
SYNOPSIS
To compile this driver into your kernel, place the following line in your kernel configura‐
tion file:
device nvme
Or, to load the driver as a module at boot, place the following line in loader.conf(5):
nvme_load="YES"
Most users will also want to enable nvd(4) to surface NVM Express namespaces as disk devices
which can be partitioned. Note that in NVM Express terms, a namespace is roughly equivalent
to a SCSI LUN.
DESCRIPTION
The nvme driver provides support for NVM Express (NVMe) controllers, such as:
· Hardware initialization
· Per-CPU IO queue pairs
· API for registering NVMe namespace consumers such as nvd(4)
· API for submitting NVM commands to namespaces
· Ioctls for controller and namespace configuration and management
The nvme driver creates controller device nodes in the format /dev/nvmeX and namespace
device nodes in the format /dev/nvmeXnsY. Note that the NVM Express specification starts
numbering namespaces at 1, not 0, and this driver follows that convention.
CONFIGURATION
By default, nvme will create an I/O queue pair for each CPU, provided enough MSI-X vectors
can be allocated. To force a single I/O queue pair shared by all CPUs, set the following
tunable value in loader.conf(5):
hw.nvme.per_cpu_io_queues=0
To force legacy interrupts for all nvme driver instances, set the following tunable value in
loader.conf(5):
hw.nvme.force_intx=1
Note that use of INTx implies disabling of per-CPU I/O queue pairs.
SYSCTL VARIABLES
The following controller-level sysctls are currently implemented:
dev.nvme.0.int_coal_time
(R/W) Interrupt coalescing timer period in microseconds. Set to 0 to disable.
dev.nvme.0.int_coal_threshold
(R/W) Interrupt coalescing threshold in number of command completions. Set to 0 to
disable.
The following queue pair-level sysctls are currently implemented. Admin queue sysctls take
the format of dev.nvme.0.adminq and I/O queue sysctls take the format of dev.nvme.0.ioq0.
dev.nvme.0.ioq0.num_entries
(R) Number of entries in this queue pair's command and completion queue.
dev.nvme.0.ioq0.num_tr
(R) Number of nvme_tracker structures currently allocated for this queue pair.
dev.nvme.0.ioq0.num_prp_list
(R) Number of nvme_prp_list structures currently allocated for this queue pair.
dev.nvme.0.ioq0.sq_head
(R) Current location of the submission queue head pointer as observed by the driver.
The head pointer is incremented by the controller as it takes commands off of the
submission queue.
dev.nvme.0.ioq0.sq_tail
(R) Current location of the submission queue tail pointer as observed by the driver.
The driver increments the tail pointer after writing a command into the submission
queue to signal that a new command is ready to be processed.
dev.nvme.0.ioq0.cq_head
(R) Current location of the completion queue head pointer as observed by the driver.
The driver increments the head pointer after finishing with a completion entry that
was posted by the controller.
dev.nvme.0.ioq0.num_cmds
(R) Number of commands that have been submitted on this queue pair.
dev.nvme.0.ioq0.dump_debug
(W) Writing 1 to this sysctl will dump the full contents of the submission and com‐
pletion queues to the console.
SEE ALSOnvd(4), pci(4), nvmecontrol(8), disk(9)HISTORY
The nvme driver first appeared in FreeBSD 9.2.
AUTHORS
The nvme driver was developed by Intel and originally written by Jim Harris
<@FreeBSD.org>, with contributions from Joe Golio at EMC.
This man page was written by Jim Harris <@FreeBSD.org>.BSD March 18, 2014 BSD